Modern factory production lines are highly efficient. The operation of production lines has developed over the years to decrease the costs of manufacturing products, primarily by decreasing the time taken to manufacture products, which in turn is achieved by increasing the throughput of articles on production lines. Such developments include, for example: carrying out tasks on a production line whilst the production line is moving; dividing the production up into small tasks, each worker carrying out one task repetitively on each article on the line; locating everything needed to carry out a task, for example accessories and tools, next to the production line where the task is to be carried out; and developing machines to carry out operations previously done by hand. All work carried out on a production line can be divided into two types of activity: the first type adds value to the final product by, for example, attaching a new component; the second type is ‘non-value-add’ work, which includes worker motion, selecting parts, and identifying parts and products to some computerized production line control system. One of the main goals of production line design is to eliminate non-value-add activities as far as possible, hence increasing the throughput of articles on the production line.
In tandem with the desire to decrease manufacturing costs of products by increasing the throughput of articles on production lines, is the desire to maintain quality control of those products. However, quality control measures generally involve testing, checking, and recording results of those tests and checks. The act of recording a result necessarily involves a non-value-add identification task, so that the tests are assigned in some computer system to the product on which they have been performed. Such measures increase the overall time taken to manufacture a product, which conflicts with the desire to minimise manufacture time.
It is often necessary to identify and/or locate an article on a production line. For example, if it is determined that an article does not meet quality control measures, then that article is identified such that it can be appropriately dealt with. Identification is a non-value-add activity, and hence it is desirable to perform identification in the minimum time possible. There are several known methods of identifying articles on production lines. In the field of vehicle manufacture, it is known to attach a tag to either the vehicle or the vehicle carrier. The tag transmits location signals comprising an identifier of the vehicle to a tracking system comprising a set of sensors mounted in the factory. This method requires the application of a tag to the vehicle or vehicle carrier. Subsequently the tag is removed. The processes of applying and removing a tag to an article on a production line are non-value-add activities. They increase the time taken to process the article on the production line, and hence reduce the throughput of articles on the production line. This is particularly problematic if several tags need to be applied and removed from an article during the manufacturing process, for example as a result of a vehicle changing vehicle carrier or changing production line. This is also problematic for small scale systems for which the time taken to apply and remove a tag is significant relative to the time that the article is on the production line. Additionally, such systems generally require extraction of information about the production line from the system controlling the production line, for example the speed of the production line. This requires some integration of the tracking system software and the production line control system software. Production line control systems are not standardised across the production line industry, hence this integration must be carried out each time the tracking system is to be operated in combination with a different production line control system.
It is also known to identify a vehicle by detecting its movement past specified locations on a production line. For example, a rotary encoder may be attached to the production line. The rotary encoder rotates through an angle proportional to the displacement of the line. Its rotation is measured and encoded by, for example, placing holes evenly spaced around its circumference and detecting each hole using a fixed light source/detector, such as a LED/photodiode combination. The location of the vehicle with respect to the production line is known, and hence the vehicle can be identified. Production line positioning using encoders is not standardised across the production line industry, hence integration tasks must be carried out each time a system is deployed in a new production line. Furthermore, such systems are only available on a small proportion of all production lines.
Thus, there is a need for a tracking system which identifies articles on a production line accurately without requiring additional non-value-add tasks on the production line, and which is suitable for application to any production line irrespective of the specific production line control system used.